perf: optimize release builds and document benchmarking

Cargo.toml

@@ -14,3 +14,8 @@ ovmf-prebuilt = "0.2.4"
 [build-dependencies]
 kernel = { path = "kernel", artifact = "bin", target = "x86_64-unknown-none" }
 bootloader = "0.11.17"
+
+[profile.release]
+opt-level = 3
+lto = "thin"
+codegen-units = 1

docs/performance.md

@@ -0,0 +1,48 @@
+# Performance validation
+
+Rustalis is an experimental OS, so performance changes should be measured rather
+than assumed. The release profile in the workspace enables maximum optimization,
+thin link-time optimization, and a single codegen unit. These settings affect
+release builds; ordinary development builds remain optimized for iteration speed.
+
+## Build
+
+Use the pinned nightly toolchain from `rust-toolchain.toml`:
+
+```sh
+cargo build --release
+```
+
+For correctness checks, continue to run:
+
+```sh
+cargo fmt --all -- --check
+cargo check --workspace
+cargo clippy --workspace --all-targets -- -D warnings
+cargo test --workspace
+```
+
+## Benchmark protocol
+
+Before claiming a speedup, record a baseline and compare it with the optimized
+build on the same host and QEMU configuration.
+
+Record at least:
+
+- Build mode and Rust toolchain version.
+- Kernel/boot-image size.
+- Time from QEMU launch to the first serial boot message.
+- Repeated measurements (at least five runs), reporting median and spread.
+- QEMU version, machine type, firmware, CPU settings, and host OS.
+
+Keep the guest workload and emulator arguments identical between runs. Separate
+build-time improvements from boot-time and runtime improvements; they measure
+different things. Do not treat a smaller binary or a faster host build as proof
+of faster kernel execution.
+
+## Next optimization targets
+
+Once the corresponding subsystems exist, benchmark serial logging overhead,
+page allocation, context switching, syscall entry/exit, and filesystem/network
+I/O independently. Avoid removing diagnostics or weakening safety checks solely
+to improve a benchmark. Keep debug builds useful for kernel development.